Noise emission from wind parks is a well-known problem and has been the subject of extensive work, both with respect to the planning of new wind parks and to the operation of existing wind parks.
One solution to prevent the emitted noise from the wind turbines of the wind park from exceeding a predetermined level at a given immission point, typically a position in a residential area, is provided in U.S. Pat. No. 6,688,841 where the sound level is measured at the immission point and is used for controlling the operation of the wind turbine, e.g. by reduction of the rotational speed of individual wind turbines so as to lower the sound level at the immission point.
It may provide difficulties to arrange a sound level measurement device at the actual immission point of interest, and in US 2007/031237 a method is disclosed for controlling noise from a wind park by monitoring noise emission from the wind turbines in a near field area and utilizing a transfer function of noise emission to determine a noise impact importance of the wind turbines at one or more locations in a far field area beyond a boundary of the wind park.
Another method which is known in the art for controlling the noise emission from a wind park involves a test period after the erection of the wind park, where the noise at a number of immission points is measured and registered together with the varying wind speed and wind direction. The measurements are utilized to form an empirical set of operational rules for the wind park control system so as to prevent the noise at the immission points caused by the wind park to exceed a given threshold level. This method eliminates the requirement for permanent sound level measurement devices arranged in or around the wind park, but the power production of the wind park will often be somewhat lowered because the regulation of the wind turbines of the wind park, typically by lowering the rotational speed of the wind turbine rotors, will need to ensure that the noise threshold is not exceeded without having a noise measurement feedback.
An object of the present invention is therefore to provide for a method for controlling the noise emission from a wind park and at the same time to optimise the operation of the wind park with respect to power production.